An electrodeless fluorescent lamp (EFL) implements a coil design in its configuration. Such a coil design includes a cylindrical ferrite core, a bobbin and conductive insulative wire wound around a portion of the bobbin. FIG. 1 illustrates a prior art high-temperature plastic threaded bobbin 10 which may be used in such a design. As depicted, bobbin 10 includes a high-temperature plastic base portion 12 and an integrated threaded high-temperature plastic chimney portion 14. Chimney portion 14 is molded to include grooves 16 on the exterior cylindrical surface. A cylindrical ferrite core, not shown, is placed within the interior 18 of chimney 14 and conductive wire (not shown) is wound around chimney 14 by following the groove pattern 16. A tape or shrink-tubing product would then be placed around the wound conductive wire to maintain the wire in position and maintain the integrity of the coil.
In the prior art coil, there are at least two ends of the conductive wire wound around the chimney 14 of bobbin 10. The ends of these wires are passed through the base 12 for attachment to an electronic board or alternatively attached to plugs attached to the underside of base 12. The plugs may be received by the electronic board for connection of the coil configuration. Threads 16 provide a built-in pitch wire spacing for the conductive wire.
Chimney 14 is a split element 20 whereby when conductive wire is wound around chimney 14 in the groove pattern 16, chimney 14 is compressed around the ferrite core. Hook or holding elements 22 act to maintain the core securely within interior 18. The underside of base 12 is formed such that the bottom portion of ferrite core is held within the chimney 14. Bobbin 10 acts as an electrically insulating layer between the conductive wire and the ferrite core sufficient to prevent electrical breakdowns from occurring within the coil. The conductive wire itself may be insulated, and capable of continually withstanding temperatures approximately 250xc2x0 C.
During operation of a coil, the highest temperature in the core body will occur in the middle height location of the core. Therefore, in FIG. 1 the area having the highest temperature on bobbin 10 would be approximately at location 24. For an RF coil assembly intended to work with EFL products in the 120-volt and 230-volt range, the temperature at this center point 24 could reach 250xc2x0. This being the case, it is necessary for bobbin 10 to be made of a material that has a maximum allowable service temperature capable of withstanding such a temperature level. Temperatures at the ends of the coil are around 200xc2x0 C.
A drawback of a coil manufactured using bobbin 10 of FIG. 1, is the requirement of using the high-temperature material in order to withstand the temperatures generated during operation of the coil. This necessitates the use of expensive high temperature materials. Further, bobbin 10 uses a significant amount of such an expensive material due to the chimney feature. Additionally there is a significant amount of cost involved in manufacturing the bobbin 10 with threads 16.
Therefore, the present invention looks to manufacture a simplified RF coil assembly with decreased costs as compared to existing coil assemblies, where the coil assembly meets expectations and operational requirements for use with an electrodeless fluorescent lamps.
A cylindrical ferrite core includes a top-end, bottom-end and inner opening extending from the top end to the bottom end. An outer surface of the cylindrical core includes a step portion formed at the bottom end of the core, extending past the outer circumference of the non-step portion. A first high dielectric material is formed over at least a substantial portion of the outer surface of the cylindrical core to provide an insulative barrier. A length of conductive wire having a first end and a second end is wound around the first high dielectric material located over the outer surface of the cylindrical ferrite core. A second high dielectric material is then placed or located over the length of the conductive wire. This configuration seals the conductive wire between the two high dielectric materials and insulating the conductive wire from the ferrite core. A coil holder is provided having a base portion with a base opening formed substantially in a centered area in the base of the coil holder, the base opening is sufficiently sized to provide a passage way to the inner opening of the ferrite core. A snap-fit portion having a plurality of snap-fit fingers extending from the base portion engage the step portion of the cylindrical ferrite core, whereby the core is locked into engagement with the coil holder.